This invention relates generally to the dissipation of heat from high power electronic devices, and more particularly to the casting of an improved heat exchanger structure within a metal matrix composite.
Heat dissipating plate and shell structures having desirable combinations of thermal conductivity, thermal expansion, and stiffness are in great demand for critical electronic applications. The heat generated in electronic components requires, in many cases, that heat sinks be used to remove the heat from the electronic device or component. Enhanced component reliability is achieved through use of heat sinks with good thermal conductivity to transfer heat away from high-density electronic components and devices such as integrated circuits. When heat sinks are not used, various other devices have been designed for direct attachment to a heat dissipating plate which, in turn, will act as a heat transfer element.
Moreover, the rapidly increasing density of integrated circuits, large-scale integrated circuits, power diodes and the like continues to create the need for improved thermal management solutions. Consequently, heat-dissipating structures have undergone continuous improvements as the electronics industry has developed. In these situations, it is often desirable to form internal cooling channels within a heat dissipating structure. Circulating fluids can then be used to more effectively remove heat from the heat-generating device mounted to the structure. This would allow for enhanced cooling efficiency and thermal stability in situations where the thermal conductivity of the heat dissipating structure alone is insufficient.
When the electronic components are attached to a heat dissipating structure, even one of the more advanced structures available today to provide good thermal conductivity, the different coefficients of thermal expansion for the various elements often cause problems. For example, the heat sink and the electrically insulating substrate, to which the electronic component is attached, may have different coefficients of thermal expansion. Similarly, different coefficients of thermal expansion may exist between the electronic component and the heat sink. When there is significant difference in coefficients of thermal expansion between components, temperature changes arising from soldering during assembly and heat generated in the systems during operation can cause large thermal stresses due to the differences in relative expansion of the materials. Such stresses may cause, in turn, premature component failure. Traditional thermal dissipation materials such as Al and Cu have CTE values that are much greater than IC devices or substrate materials. Therefore, the IC package typically includes a marginally compatible CTE interface, such as a high thermal resistivity Al2O3 substrate, to provide a stress-reducing interface. The solution presents a thermal penalty and often a reliability penalty in the form of cracked Al2O3 substrates. Traditional CTE-compatible packaging materials, such as Kovar and various other Nixe2x80x94Fe alloys, have low thermal conductivity. More advanced packaging materials such as CuMo and CuW offer high thermal conductivity and compatible CTE values but are heavy and costly to fabricate in all but simple flat plate shapes. Aluminum Silicon Carbide (AlSiC) packages offer desirable packaging attributes of compatible CTE value and high thermal conductivity. An AlSiC heat dissipating structure is lightweight making it desirable for portable devices and airborne, spaceborne or any other weight sensitive application.
The present invention pertains to a fluid flow heat exchanger cast in a metal matrix composite and method of making the same. The method comprises the steps of 1.) positioning an insert within a mold chamber of a closed mold 2.) filling the closed mold with a preform reinforcement material such that the insert is completely encased or xe2x80x9covermoldedxe2x80x9d within the preform material, and 3.) infiltrating the preform and insert with a liquid metal and allowing for the metal to solidify to form a metal matrix composite. The process of filling the closed mold containing the insert with preform reinforcement material allows for intimate contact between the insert and the reinforcement material. Enhanced thermal and mechanical properties are realized by eliminating voids or gaps at this reinforcement material-to-tube interface. In one embodiment, the insert comprises a stainless steel hollow core closed at both ends. After the metal infiltration process is complete the closed ends of the tubes are opened to allow for liquid fluid flow through the metal matrix composite. In one embodiment, the metal matrix composite encasing the insert is comprised of an Aluminum Silicon Carbide (AlSiC) housing offering a unique set of material properties that are suited to high performance advanced thermal management packaging designs. AlSiC is a composite material of Al-metal and SiC particulate. Thermal conductivity values for Al/SiC materials are similar to Al metal and the AlSiC CTE values are compatible with direct device attachment. Furthermore, AlSiC CTE can be designed to fit the requirements of the specific application. Changing of the Al/SiC ratio and/or the Al-metal composition can modify the CTE to be compatible with the CTE of the heat-generating device mounted thereon.